/* * Copyright (c) 2007, 2012, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 only, as * published by the Free Software Foundation. * * This code is distributed in the hope that it will be useful, but WITHOUT * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License * version 2 for more details (a copy is included in the LICENSE file that * accompanied this code). * * You should have received a copy of the GNU General Public License version * 2 along with this work; if not, write to the Free Software Foundation, * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. * * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. * */ #include "precompiled.hpp" #include "memory/allocation.inline.hpp" #include "memory/cardTableModRefBS.hpp" #include "memory/cardTableRS.hpp" #include "memory/sharedHeap.hpp" #include "memory/space.inline.hpp" #include "memory/universe.hpp" #include "oops/oop.inline.hpp" #include "runtime/java.hpp" #include "runtime/mutexLocker.hpp" #include "runtime/virtualspace.hpp" #include "runtime/vmThread.hpp" void CardTableModRefBS::non_clean_card_iterate_parallel_work(Space* sp, MemRegion mr, OopsInGenClosure* cl, CardTableRS* ct, int n_threads) { assert(n_threads > 0, "Error: expected n_threads > 0"); assert((n_threads == 1 && ParallelGCThreads == 0) || n_threads <= (int)ParallelGCThreads, "# worker threads != # requested!"); assert(!Thread::current()->is_VM_thread() || (n_threads == 1), "There is only 1 VM thread"); assert(UseDynamicNumberOfGCThreads || !FLAG_IS_DEFAULT(ParallelGCThreads) || n_threads == (int)ParallelGCThreads, "# worker threads != # requested!"); // Make sure the LNC array is valid for the space. jbyte** lowest_non_clean; uintptr_t lowest_non_clean_base_chunk_index; size_t lowest_non_clean_chunk_size; get_LNC_array_for_space(sp, lowest_non_clean, lowest_non_clean_base_chunk_index, lowest_non_clean_chunk_size); uint n_strides = n_threads * ParGCStridesPerThread; SequentialSubTasksDone* pst = sp->par_seq_tasks(); // Sets the condition for completion of the subtask (how many threads // need to finish in order to be done). pst->set_n_threads(n_threads); pst->set_n_tasks(n_strides); uint stride = 0; while (!pst->is_task_claimed(/* reference */ stride)) { process_stride(sp, mr, stride, n_strides, cl, ct, lowest_non_clean, lowest_non_clean_base_chunk_index, lowest_non_clean_chunk_size); } if (pst->all_tasks_completed()) { // Clear lowest_non_clean array for next time. intptr_t first_chunk_index = addr_to_chunk_index(mr.start()); uintptr_t last_chunk_index = addr_to_chunk_index(mr.last()); for (uintptr_t ch = first_chunk_index; ch <= last_chunk_index; ch++) { intptr_t ind = ch - lowest_non_clean_base_chunk_index; assert(0 <= ind && ind < (intptr_t)lowest_non_clean_chunk_size, "Bounds error"); lowest_non_clean[ind] = NULL; } } } void CardTableModRefBS:: process_stride(Space* sp, MemRegion used, jint stride, int n_strides, OopsInGenClosure* cl, CardTableRS* ct, jbyte** lowest_non_clean, uintptr_t lowest_non_clean_base_chunk_index, size_t lowest_non_clean_chunk_size) { // We go from higher to lower addresses here; it wouldn't help that much // because of the strided parallelism pattern used here. // Find the first card address of the first chunk in the stride that is // at least "bottom" of the used region. jbyte* start_card = byte_for(used.start()); jbyte* end_card = byte_after(used.last()); uintptr_t start_chunk = addr_to_chunk_index(used.start()); uintptr_t start_chunk_stride_num = start_chunk % n_strides; jbyte* chunk_card_start; if ((uintptr_t)stride >= start_chunk_stride_num) { chunk_card_start = (jbyte*)(start_card + (stride - start_chunk_stride_num) * ParGCCardsPerStrideChunk); } else { // Go ahead to the next chunk group boundary, then to the requested stride. chunk_card_start = (jbyte*)(start_card + (n_strides - start_chunk_stride_num + stride) * ParGCCardsPerStrideChunk); } while (chunk_card_start < end_card) { // Even though we go from lower to higher addresses below, the // strided parallelism can interleave the actual processing of the // dirty pages in various ways. For a specific chunk within this // stride, we take care to avoid double scanning or missing a card // by suitably initializing the "min_done" field in process_chunk_boundaries() // below, together with the dirty region extension accomplished in // DirtyCardToOopClosure::do_MemRegion(). jbyte* chunk_card_end = chunk_card_start + ParGCCardsPerStrideChunk; // Invariant: chunk_mr should be fully contained within the "used" region. MemRegion chunk_mr = MemRegion(addr_for(chunk_card_start), chunk_card_end >= end_card ? used.end() : addr_for(chunk_card_end)); assert(chunk_mr.word_size() > 0, "[chunk_card_start > used_end)"); assert(used.contains(chunk_mr), "chunk_mr should be subset of used"); DirtyCardToOopClosure* dcto_cl = sp->new_dcto_cl(cl, precision(), cl->gen_boundary()); ClearNoncleanCardWrapper clear_cl(dcto_cl, ct); // Process the chunk. process_chunk_boundaries(sp, dcto_cl, chunk_mr, used, lowest_non_clean, lowest_non_clean_base_chunk_index, lowest_non_clean_chunk_size); // We want the LNC array updates above in process_chunk_boundaries // to be visible before any of the card table value changes as a // result of the dirty card iteration below. OrderAccess::storestore(); // We do not call the non_clean_card_iterate_serial() version because // we want to clear the cards: clear_cl here does the work of finding // contiguous dirty ranges of cards to process and clear. clear_cl.do_MemRegion(chunk_mr); // Find the next chunk of the stride. chunk_card_start += ParGCCardsPerStrideChunk * n_strides; } } // If you want a talkative process_chunk_boundaries, // then #define NOISY(x) x #ifdef NOISY #error "Encountered a global preprocessor flag, NOISY, which might clash with local definition to follow" #else #define NOISY(x) #endif void CardTableModRefBS:: process_chunk_boundaries(Space* sp, DirtyCardToOopClosure* dcto_cl, MemRegion chunk_mr, MemRegion used, jbyte** lowest_non_clean, uintptr_t lowest_non_clean_base_chunk_index, size_t lowest_non_clean_chunk_size) { // We must worry about non-array objects that cross chunk boundaries, // because such objects are both precisely and imprecisely marked: // .. if the head of such an object is dirty, the entire object // needs to be scanned, under the interpretation that this // was an imprecise mark // .. if the head of such an object is not dirty, we can assume // precise marking and it's efficient to scan just the dirty // cards. // In either case, each scanned reference must be scanned precisely // once so as to avoid cloning of a young referent. For efficiency, // our closures depend on this property and do not protect against // double scans. uintptr_t cur_chunk_index = addr_to_chunk_index(chunk_mr.start()); cur_chunk_index = cur_chunk_index - lowest_non_clean_base_chunk_index; NOISY(tty->print_cr("===========================================================================");) NOISY(tty->print_cr(" process_chunk_boundary: Called with [" PTR_FORMAT "," PTR_FORMAT ")", chunk_mr.start(), chunk_mr.end());) // First, set "our" lowest_non_clean entry, which would be // used by the thread scanning an adjoining left chunk with // a non-array object straddling the mutual boundary. // Find the object that spans our boundary, if one exists. // first_block is the block possibly straddling our left boundary. HeapWord* first_block = sp->block_start(chunk_mr.start()); assert((chunk_mr.start() != used.start()) || (first_block == chunk_mr.start()), "First chunk should always have a co-initial block"); // Does the block straddle the chunk's left boundary, and is it // a non-array object? if (first_block < chunk_mr.start() // first block straddles left bdry && sp->block_is_obj(first_block) // first block is an object && !(oop(first_block)->is_objArray() // first block is not an array (arrays are precisely dirtied) || oop(first_block)->is_typeArray())) { // Find our least non-clean card, so that a left neighbour // does not scan an object straddling the mutual boundary // too far to the right, and attempt to scan a portion of // that object twice. jbyte* first_dirty_card = NULL; jbyte* last_card_of_first_obj = byte_for(first_block + sp->block_size(first_block) - 1); jbyte* first_card_of_cur_chunk = byte_for(chunk_mr.start()); jbyte* last_card_of_cur_chunk = byte_for(chunk_mr.last()); jbyte* last_card_to_check = (jbyte*) MIN2((intptr_t) last_card_of_cur_chunk, (intptr_t) last_card_of_first_obj); // Note that this does not need to go beyond our last card // if our first object completely straddles this chunk. for (jbyte* cur = first_card_of_cur_chunk; cur <= last_card_to_check; cur++) { jbyte val = *cur; if (card_will_be_scanned(val)) { first_dirty_card = cur; break; } else { assert(!card_may_have_been_dirty(val), "Error"); } } if (first_dirty_card != NULL) { NOISY(tty->print_cr(" LNC: Found a dirty card at " PTR_FORMAT " in current chunk", first_dirty_card);) assert(0 <= cur_chunk_index && cur_chunk_index < lowest_non_clean_chunk_size, "Bounds error."); assert(lowest_non_clean[cur_chunk_index] == NULL, "Write exactly once : value should be stable hereafter for this round"); lowest_non_clean[cur_chunk_index] = first_dirty_card; } NOISY(else { tty->print_cr(" LNC: Found no dirty card in current chunk; leaving LNC entry NULL"); // In the future, we could have this thread look for a non-NULL value to copy from its // right neighbour (up to the end of the first object). if (last_card_of_cur_chunk < last_card_of_first_obj) { tty->print_cr(" LNC: BEWARE!!! first obj straddles past right end of chunk:\n" " might be efficient to get value from right neighbour?"); } }) } else { // In this case we can help our neighbour by just asking them // to stop at our first card (even though it may not be dirty). NOISY(tty->print_cr(" LNC: first block is not a non-array object; setting LNC to first card of current chunk");) assert(lowest_non_clean[cur_chunk_index] == NULL, "Write once : value should be stable hereafter"); jbyte* first_card_of_cur_chunk = byte_for(chunk_mr.start()); lowest_non_clean[cur_chunk_index] = first_card_of_cur_chunk; } NOISY(tty->print_cr(" process_chunk_boundary: lowest_non_clean[" INTPTR_FORMAT "] = " PTR_FORMAT " which corresponds to the heap address " PTR_FORMAT, cur_chunk_index, lowest_non_clean[cur_chunk_index], (lowest_non_clean[cur_chunk_index] != NULL) ? addr_for(lowest_non_clean[cur_chunk_index]) : NULL);) NOISY(tty->print_cr("---------------------------------------------------------------------------");) // Next, set our own max_to_do, which will strictly/exclusively bound // the highest address that we will scan past the right end of our chunk. HeapWord* max_to_do = NULL; if (chunk_mr.end() < used.end()) { // This is not the last chunk in the used region. // What is our last block? We check the first block of // the next (right) chunk rather than strictly check our last block // because it's potentially more efficient to do so. HeapWord* const last_block = sp->block_start(chunk_mr.end()); assert(last_block <= chunk_mr.end(), "In case this property changes."); if ((last_block == chunk_mr.end()) // our last block does not straddle boundary || !sp->block_is_obj(last_block) // last_block isn't an object || oop(last_block)->is_objArray() // last_block is an array (precisely marked) || oop(last_block)->is_typeArray()) { max_to_do = chunk_mr.end(); NOISY(tty->print_cr(" process_chunk_boundary: Last block on this card is not a non-array object;\n" " max_to_do left at " PTR_FORMAT, max_to_do);) } else { assert(last_block < chunk_mr.end(), "Tautology"); // It is a non-array object that straddles the right boundary of this chunk. // last_obj_card is the card corresponding to the start of the last object // in the chunk. Note that the last object may not start in // the chunk. jbyte* const last_obj_card = byte_for(last_block); const jbyte val = *last_obj_card; if (!card_will_be_scanned(val)) { assert(!card_may_have_been_dirty(val), "Error"); // The card containing the head is not dirty. Any marks on // subsequent cards still in this chunk must have been made // precisely; we can cap processing at the end of our chunk. max_to_do = chunk_mr.end(); NOISY(tty->print_cr(" process_chunk_boundary: Head of last object on this card is not dirty;\n" " max_to_do left at " PTR_FORMAT, max_to_do);) } else { // The last object must be considered dirty, and extends onto the // following chunk. Look for a dirty card in that chunk that will // bound our processing. jbyte* limit_card = NULL; const size_t last_block_size = sp->block_size(last_block); jbyte* const last_card_of_last_obj = byte_for(last_block + last_block_size - 1); jbyte* const first_card_of_next_chunk = byte_for(chunk_mr.end()); // This search potentially goes a long distance looking // for the next card that will be scanned, terminating // at the end of the last_block, if no earlier dirty card // is found. assert(byte_for(chunk_mr.end()) - byte_for(chunk_mr.start()) == ParGCCardsPerStrideChunk, "last card of next chunk may be wrong"); for (jbyte* cur = first_card_of_next_chunk; cur <= last_card_of_last_obj; cur++) { const jbyte val = *cur; if (card_will_be_scanned(val)) { NOISY(tty->print_cr(" Found a non-clean card " PTR_FORMAT " with value 0x%x", cur, (int)val);) limit_card = cur; break; } else { assert(!card_may_have_been_dirty(val), "Error: card can't be skipped"); } } if (limit_card != NULL) { max_to_do = addr_for(limit_card); assert(limit_card != NULL && max_to_do != NULL, "Error"); NOISY(tty->print_cr(" process_chunk_boundary: Found a dirty card at " PTR_FORMAT " max_to_do set at " PTR_FORMAT " which is before end of last block in chunk: " PTR_FORMAT " + " PTR_FORMAT " = " PTR_FORMAT, limit_card, max_to_do, last_block, last_block_size, (last_block+last_block_size));) } else { // The following is a pessimistic value, because it's possible // that a dirty card on a subsequent chunk has been cleared by // the time we get to look at it; we'll correct for that further below, // using the LNC array which records the least non-clean card // before cards were cleared in a particular chunk. limit_card = last_card_of_last_obj; max_to_do = last_block + last_block_size; assert(limit_card != NULL && max_to_do != NULL, "Error"); NOISY(tty->print_cr(" process_chunk_boundary: Found no dirty card before end of last block in chunk\n" " Setting limit_card to " PTR_FORMAT " and max_to_do " PTR_FORMAT " + " PTR_FORMAT " = " PTR_FORMAT, limit_card, last_block, last_block_size, max_to_do);) } assert(0 < cur_chunk_index+1 && cur_chunk_index+1 < lowest_non_clean_chunk_size, "Bounds error."); // It is possible that a dirty card for the last object may have been // cleared before we had a chance to examine it. In that case, the value // will have been logged in the LNC for that chunk. // We need to examine as many chunks to the right as this object // covers. However, we need to bound this checking to the largest // entry in the LNC array: this is because the heap may expand // after the LNC array has been created but before we reach this point, // and the last block in our chunk may have been expanded to include // the expansion delta (and possibly subsequently allocated from, so // it wouldn't be sufficient to check whether that last block was // or was not an object at this point). uintptr_t last_chunk_index_to_check = addr_to_chunk_index(last_block + last_block_size - 1) - lowest_non_clean_base_chunk_index; const uintptr_t last_chunk_index = addr_to_chunk_index(used.last()) - lowest_non_clean_base_chunk_index; if (last_chunk_index_to_check > last_chunk_index) { assert(last_block + last_block_size > used.end(), err_msg("Inconsistency detected: last_block [" PTR_FORMAT "," PTR_FORMAT "]" " does not exceed used.end() = " PTR_FORMAT "," " yet last_chunk_index_to_check " INTPTR_FORMAT " exceeds last_chunk_index " INTPTR_FORMAT, last_chunk_index_to_check, last_chunk_index)); assert(sp->used_region().end() > used.end(), err_msg("Expansion did not happen: " "[" PTR_FORMAT "," PTR_FORMAT ") -> [" PTR_FORMAT "," PTR_FORMAT ")", sp->used_region().start(), sp->used_region().end(), used.start(), used.end())); NOISY(tty->print_cr(" process_chunk_boundary: heap expanded; explicitly bounding last_chunk");) last_chunk_index_to_check = last_chunk_index; } for (uintptr_t lnc_index = cur_chunk_index + 1; lnc_index <= last_chunk_index_to_check; lnc_index++) { jbyte* lnc_card = lowest_non_clean[lnc_index]; if (lnc_card != NULL) { // we can stop at the first non-NULL entry we find if (lnc_card <= limit_card) { NOISY(tty->print_cr(" process_chunk_boundary: LNC card " PTR_FORMAT " is lower than limit_card " PTR_FORMAT, " max_to_do will be lowered to " PTR_FORMAT " from " PTR_FORMAT, lnc_card, limit_card, addr_for(lnc_card), max_to_do);) limit_card = lnc_card; max_to_do = addr_for(limit_card); assert(limit_card != NULL && max_to_do != NULL, "Error"); } // In any case, we break now break; } // else continue to look for a non-NULL entry if any } assert(limit_card != NULL && max_to_do != NULL, "Error"); } assert(max_to_do != NULL, "OOPS 1 !"); } assert(max_to_do != NULL, "OOPS 2!"); } else { max_to_do = used.end(); NOISY(tty->print_cr(" process_chunk_boundary: Last chunk of this space;\n" " max_to_do left at " PTR_FORMAT, max_to_do);) } assert(max_to_do != NULL, "OOPS 3!"); // Now we can set the closure we're using so it doesn't to beyond // max_to_do. dcto_cl->set_min_done(max_to_do); #ifndef PRODUCT dcto_cl->set_last_bottom(max_to_do); #endif NOISY(tty->print_cr("===========================================================================\n");) } #undef NOISY void CardTableModRefBS:: get_LNC_array_for_space(Space* sp, jbyte**& lowest_non_clean, uintptr_t& lowest_non_clean_base_chunk_index, size_t& lowest_non_clean_chunk_size) { int i = find_covering_region_containing(sp->bottom()); MemRegion covered = _covered[i]; size_t n_chunks = chunks_to_cover(covered); // Only the first thread to obtain the lock will resize the // LNC array for the covered region. Any later expansion can't affect // the used_at_save_marks region. // (I observed a bug in which the first thread to execute this would // resize, and then it would cause "expand_and_allocate" that would // increase the number of chunks in the covered region. Then a second // thread would come and execute this, see that the size didn't match, // and free and allocate again. So the first thread would be using a // freed "_lowest_non_clean" array.) // Do a dirty read here. If we pass the conditional then take the rare // event lock and do the read again in case some other thread had already // succeeded and done the resize. int cur_collection = Universe::heap()->total_collections(); if (_last_LNC_resizing_collection[i] != cur_collection) { MutexLocker x(ParGCRareEvent_lock); if (_last_LNC_resizing_collection[i] != cur_collection) { if (_lowest_non_clean[i] == NULL || n_chunks != _lowest_non_clean_chunk_size[i]) { // Should we delete the old? if (_lowest_non_clean[i] != NULL) { assert(n_chunks != _lowest_non_clean_chunk_size[i], "logical consequence"); FREE_C_HEAP_ARRAY(CardPtr, _lowest_non_clean[i], mtGC); _lowest_non_clean[i] = NULL; } // Now allocate a new one if necessary. if (_lowest_non_clean[i] == NULL) { _lowest_non_clean[i] = NEW_C_HEAP_ARRAY(CardPtr, n_chunks, mtGC); _lowest_non_clean_chunk_size[i] = n_chunks; _lowest_non_clean_base_chunk_index[i] = addr_to_chunk_index(covered.start()); for (int j = 0; j < (int)n_chunks; j++) _lowest_non_clean[i][j] = NULL; } } _last_LNC_resizing_collection[i] = cur_collection; } } // In any case, now do the initialization. lowest_non_clean = _lowest_non_clean[i]; lowest_non_clean_base_chunk_index = _lowest_non_clean_base_chunk_index[i]; lowest_non_clean_chunk_size = _lowest_non_clean_chunk_size[i]; }